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Yellowstone National Park's bison have come a long way since 1901, when only 44 survivors of North America's millions grazed inside its boundaries. Stu Coleman, chief of the park's natural resources branch, estimates the current population at 4,300 - nearly a hundred times that number - and calls the place "a bison-generating machine."

In 1988-89, when Montana hunters shot 569 shaggy escapees from the park's northern range, the news photos were gory and a national outcry was raised. This winter looks even worse: Bison are now popping out of Yellowstone's east and west boundaries as well, and Coleman fears that a hard winter could drive as many as several thousand out of the park in the coming months. By early December the death toll already stood at 36.

Until the mid-1960s, Yellowstone bison were culled to keep their numbers in check. Since the National Park Service embarked on its "natural regulation" experiment, however, the population has been exploding. Increased winter recreation in Yellowstone has also provided hard-packed snowmobile routes on which the animals can walk right out of the park.

Once they cross its boundaries, bison are likely to find themselves on the wrong end of a state game warden's rifle barrel whenever they approach private property or livestock. Of major concern in the cattle-raising states around the park is brucellosis, a disease carried by bison which can cause cattle to abort their calves.

According to Don Bosman, Wyoming's state veterinarian, a nation-wide brucellosis eradication program is finally on the verge of success. Yellowstone's neighbors - Idaho, Montana and Wyoming - have all been certified brucellosis-free, but Bosman's Montana counterpart, Clarence Siroky, fears that its infected wildlife (elk here are also carriers) could cause other states to impose costly testing requirements on cattle shipped out of the region. Ironically, scientists generally agree that bison caught the disease from domestic livestock in the first place.

While there has never been a documented case of bison passing the infection to cattle on the open range, Bosman notes, "absence of proof doesn't mean that it's not happening." And Siroky fears that as more and more bison come out of the park, it will be impossible to keep them segregated enough from cattle to avoid contagion. He says, "It's not a question of if, but when."

Yellowstone Park's Coleman does not agree that "we have this pit of pestilence." He suspects the park's wild bovines may have a natural immunity to brucellosis. "It hasn't hurt their population here."

Coleman says that blood-serum tests for brucellosis, which show 53 percent of Yellowstone's herd to be infected, are not as accurate in buffalo as in cattle. Follow-up tissue culture tests reveal that few bison are actually contagious.

Montana's Siroky dismisses this claim as "balderdash," arguing that cattle tested under the same conditions would give similar results.

Also of concern is the impact on private property from beasts that can smash a fence flat with their 2,000 pounds. Bernie Kuntz, regional information officer for Montana's Fish, Wildlife and Parks Department in Bozeman, says his agency has had continual complaints from landowners. "Bison chase their horses, go through fences, and rub the siding off their houses."

John Emmerich, Wyoming Game and Fish Department wildlife management coordinator in Cody, says most people in his area were happy to see the bison, but he fears that the animals could compete with species like bighorn sheep for grass.

Emmerich is working on a state management plan for the bison that wander across Yellowstone's eastern boundary into Wyoming; one option, he says, might be hunting the animals.

Meanwhile, the National Park Service, the U.S. Forest Service, and Montana are putting together a long-range management plan for bison that drift into that state.

According to John Varley, director of Yellowstone's Center for Resources, options include: continuing the status quo, letting the bison range freely, closing snowmobile trails, and "some mix and match."

Native Americans, who find the practice of gunning down the errant bison repugnant, have proposed taking disease-free animals from Yellowstone's surplus to start their own herds. Some of the inter-agency alternatives, Varley says, include such a program. The Park Service has already rejected one U.S. Department of Agriculture proposal: to wipe out the infected Yellowstone herd and replace it with brucellosis-free animals. "You'd have to nuke the ecosystem," Varley says.

The real issue, most observers agree, is too many bison. Ever since 1969, park bison numbers have been doubling about every 10 years. "Where are you going to put 50,000 buffalo?" asks Wyoming's Bosman.

Coleman says the park is not opposed to controlling bison within its borders. "But," he says, "it's got to be done with some class, and some reverence for the animal."